Horizontal deflection system for cathode ray tubes



R. C. MOORE Aug. 18, 1959 HORIZONTAL DEFLECTION SYSTEM FOR CATHODE RAY TUBES Filed Oct. 31, 1956 2,900,555 Patented Aug. 18, 1959 HORIZONTAL DEFLECTION SYSTEM FOR CATHODE RAY TUBES Robert C. Moore, Huntingdon Valley, Pa., assignor to Philco Corporation, Philadelphia, Pa, a corporation of Pennsylvania Application October 31, 1956, Serial No. 619,467 6 Claims. (Cl. 315-27) This invention relates to horizontal deflection systems for cathode ray tubes, and more particularly to improvement of linearity in such systems.

In horizontal deflection systems of the type commonly employed in television receivers, horizontal deflection cur-- rent is supplied to the horizontal deflection coils of the yoke by the cooperative functioning of a driver tube, an output transformer, and a damper diode. While it is desired to provide substantial linearity of the deflection current in the horizontal deflection coils, in the absence of some additional provision toward that end the deflection current tends to be non-linear during the scan intervals. More particularly, the deflection current waveform tends to be exponential rather than linear during each scan interval, its slope being relatively larger at the beginning and relatively smaller at the end of each scan interval. This tends to make the line scanning motion of the electron beam too fast at the beginning and too slow at the end of each line scan for best picture geometry.

It is Well known that this objection can be overcome by producing a correcting voltage effective to modify the current flow through the damper diode and the yoke. Since the deflection current during scan or trace intervals is the algebraic sum of the transformed output current of the driver tube and the current through the damper tube, the deflection current can be rendered substantially linear by appropriate modification of the current through the damper tube. Accordingly, proposals have been made heretofore to develop a corrective voltage directly from the output current and/ or the damper current by the provision of additional circuit components. However, such prior proposals have not been entirely satisfactory because the corrective means are highly susceptible to variations in current waveform from which the corrective voltage is developed.

One object of the present invention is to overcome the objections of prior systems of the general character above mentioned, and to provide improved means for effecting substantial linearity through control of the damper current.

Another object of the invention is to provide simple, eflicient and inexpensive means for effecting substantial linearity in such a system.

The details of operation of a horizontal deflection sys tem of the type here involved are well known, and it is unnecessary to describe such details. It suffices to note that during the retrace portions of successive operating cycles, time-spaced voltage pulses are produced across the windings of the output transformer. The present invention is based upon the concept of utilizing these pulses to develop a linearity correction voltage. In accordance with this invention, voltage pulses are derived from the output transformer and are converted into a corrective voltage which is utilized to modify the damper current so as to effect the desired linearity correction. In the preferred embodiment of the invention, an auxiliary winding is provided on the output transformer to derive the voltage pulses, and these pulses are applied to a circuit which includes an inductor and a resistor connected in series, the resistor also being in circuit with the damper diode. The inductor integrates the voltage pulses into a current of desired waveform, which flows through the resistor and produces the desired corrective voltage. The latter effects the desired modification of the damper current to achieve substantial linearity of the deflection current.

The invention may be fully understood from the following detailed description with reference to the accompanying drawing, wherein the single figure is a diagrammatic illustration of a horizontal deflection system for a cathode ray tube embodying the present invention.

Referring more particularly to the drawing, the horizontal deflection system comprises essentially the driver tube 10, the output transformer 11, the damper diode 12, and horizontal deflection coils represented at 13, such coils forming part of the deflection yoke for the cathode ray tube 14. For simplicity, a single deflection coil is shown, but it will be understood that the deflection yoke actually has two such coils in series or parallel. The anode of the driver tube 10 is connected to a point on the winding 15 of transformer 11. The damper tube 12 is connected across a portion of the transformer winding 15 through a capacitor 16. The horizontal deflection coils 13 may be connected across the same portion of the transformer winding.

Disregarding for the moment the other elements of the system not mentioned thus far, in operation of such a horizontal deflection system, a signal such as represented at 17, is supplied to the control grid of the driver tube 11), and the latter serves as a switch to control the supply of energy to the horizontal deflection coils 13 through transformer 11. Both the driver tube 10 and the damper diode 12 are conductive during at least a portion of each trace interval, and as mentioned before, the deflection current in the horizontal deflection coils is the algebraic sum of the transformed output current of tube 10 and the damper current. During retrace, the energy stored in the horizontal deflection coils 13 of the yoke is transferredto the transformer 11 and produces a voltage pulse across the transformer winding. As the operation of a system of this character is well understood by those skilled in the art, it is unnecessary to describe the operation in further detail.

In accordance with the present invention, voltage pulses are derived from the transformer 11 and are converted into a corrective voltage which is applied to the damper diode 12 to effect substantial linearity of the deflection current in the horizontal deflection coils 13, as hereinbefore mentioned. In the preferred embodiment of the invention, as illustrated in the drawing, an auxiliary winding 18 is provided on the transformer 11 to derive the voltage pulses represented at 19. An inductor 20 and a resistor 21 are serially included in circuit with winding 18, and the resistor 21 is also in circuit with the damper diode as shown. The voltage pulses 19 are integrated by the inductor 20 into a current of desired waveform, and this current flowing through resistor 21 produces at the plate of diode 12 the desired corrective voltage. This voltage modifies the current flow through the diode so as to effect linearity correction as previously described.

Preferably, although not necessarily, an inductor 22 and a capacitor 23 are connected in shunt with the resistor 21 to improve the linearity correction. As mentioned at the outset, the uncorrected deflection waveform is exponential, and therefore for best correction the corrective voltage should be of complementary non-linear form. Elements 22 and 23 serve to impart such form to the corrective voltage.

A system according to the present invention, such as illustrated in the drawing, is characterized in that the corrective voltage is effectively derived from the yoke voltage which is much more stable than theoutput and damper currents which were previously used directly to derive a corrective voltage. Therefore, the present invention achieves better linearity correction than prior devices for the same purpose.

Considering more particularly the manner in which the present invention achieves substantial linearity of the deflection waveform, the integration of the pulses 19 by the inductor 20 produces a sawtooth current which is opposite in phase to the sawtooth deflection current, i.e. it decreases from a maximum during each scan interval. This current flowing through resistor 21 produces a corresponding sawtooth voltage in series with the damper tube 12. I The tendency toward the aforementioned non-linearity of the deflection current waveform is due to the fact that the resistance of the deflection coil-damper tube combination is inherently high in relation to inductance, and the introduction of the opposite-phase sawtooth voltage across resistor 21 simulates the introduction of a negative resistance and thus decreases the eflective resistance of said combination, resulting in linearizati'on of the deflection waveform.

In one physical embodiment of the system illustrated in the drawing, the elements 20 to 23 have values as follows:

Inductor 20 .5 to 3 millihenries. Resistor 21 68 ohms.

Inductor 22 .1 to .5 millihenry. Capacitor 23 .33 microfarad.

While apreferred embodiment of the invention has been illustrated and described, the invention is not limited thereto but contemplates such modifications and other embodiments as may occur to those skilled in the art.

I claim:

1. In a horizontal deflection system for eflecting horizontal scanning in a cathode ray tube, a grid-controlled driver tube to the control grid of which a driving voltage is supplied, an output transformer connected to said driver tube, a deflection yoke for said cathode ray tube having horizontal deflection coils connected to said transformer to receive energy therefrom, a damper diode connected to said transformer and to said coils, the aforementioned elements producing deflection current in said coils which tends to be non-linear, there-being timespaced voltage pulses produced across said transformer during retrace portions of successive operating cycles, means for deriving such voltage pulses from said transformer during successive operating cycles, means for integrating said derived pulses into a desired current, and means for deriving a corrective voltage from the latter current and for applying such voltage to said diode to effect substantial linearity of the deflection current in said coils.

2. A horizontal deflection system according to claim 1,

wherein the means for deriving voltage pulses comprises an auxiliary winding on said transformer, the means for integrating said pulses comprises an inductor in circuit with said auxiliary winding, and the means for deriving and applying a corrective voltage comprises a resistor in series with said inductor and also in series with said diode.

3. A horizontal deflection system according to claim 2, further including an inductor and a capacitor in shunt with said resistor.

4. Ina horizontal deflection system for effecting horizontal scanning in a cathode ray tube, a deflection yoke for said cathode ray tube having horizontal deflection coils, a transformer through which energy is supplied to said coils to produce deflection current therein, a damper tube connected in shunt with a portion of said transformer, there being time-spaced voltage pulses produced across said transformer during retrace portions of successive operating cycles, a resistor seriallyincluded with said damper tube in the shunt connection thereof across a portion of said transformer, and a circuit including an'auxi'liary winding on said transformer, an inductor and said resistor all in series, whereby said time-spaced voltage pulses are derived by said winding and integrated by said inductor into a current which flows through said resistor 'to produce thereacross'a corrective voltage for effecting substantial linearity of the'deflection current in said coils.

5. A horizontal deflection system "according to' claim 4, further including an inductor and a capacitor in shunt with said resistor.

6. In a deflection systemfor effecting line scanning in a cathode ray tube, a deflection circuit including an output transformer and deflection coilsand a damper tube connected to said transformer, wherein due to relatively high resistance of the. combination of the deflection coils and the damper tube in relation to inductance the slope of the sawtooth deflection current waveform tends to be relatively larger at the beginning and relatively smaller at the end of eachscan interval,,there being time-spaced voltage pulses produced across said transformer during retrace portions of successive operating cycles, a resistor in series with said damper tube, means for deriving said voltage pulses from said transformer during successive operating cycles, and means for integrating said pulses into a sawtooth current and for passing said current through said resistor, thereby to introduce in series with said damper tube a sawtooth voltage opposite in phase to the sawtooth deflectioncurrent and thus effect linearization of the deflection current waveform.

, References Citedin the file of this patent UNITED STATES PATENTS 

